1. Field of the Invention
The present invention relates to, for example, a variable frequency clock output circuit and apparatus preferably used to accelerate/decelerate a paper conveyance motor or the like for use in image forming apparatuses. It also relates to a motor driving apparatus and an image forming apparatus.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
For example, in image forming apparatuses, such as, e.g., MFP (Multi Function Peripherals) which are multifunction digital complex machines, a plurality of stepping motors are used to convey papers on which image data is to be printed and/or drive various mechanisms.
In such an image forming apparatus, in order to attain synchronization with imaging process for printing, register adjustment for full color printing, etc., it is required to control the speed (revolving speed) of the plurality of stepping motors with a high degree of accuracy. In addition, in order to meet the recent need of the productivity improvement and the image quality improvement for printing, it is also required to convey a paper at a stable rate when being printed and at the highest rate when not being printed.
A rough change in drive frequency at the time of accelerating/decelerating a stepping motor causes an increased risk of loss of synchronism (loss of synchronism between the control clock and the revolution) of the stepping motor. Therefore, in order to secure a margin against the loss of synchronism, it is required to change the drive frequency smoothly with a high degree of accuracy.
As will be understood from the above, in image forming apparatuses, etc., it is required to simultaneously accelerate/decelerate a plurality of stepping motors at different acceleration to different target revolution speeds with a high degree of accuracy. Thus, it has been desired to provide a variable frequency clock output circuit for motor driving which meets the above requests.
Conventionally, such variable frequency clocks were generated by software processing using a plurality of CPUs, memories, etc., which required complex structure and large software control load.
To cope with the aforementioned problems, Japanese Unexamined Laid-open Patent Publication No. H09-148896 proposes a clock output circuit capable of outputting a pulse signal having an arbitrary frequency without requiring interrupt processing to a CPU and/or a large memory space.
In this clock output circuit, a reference clock signal Fc is divided at previously set dividing ratio then outputted by a divider circuit, a basic clock signal Fb which is an output of the divider circuit is inputted into an acceleration/deceleration circuit, and an output signal Fout which is a pulse signal obtained by further dividing the basic clock signal Fb is outputted by the acceleration/deceleration circuit. The frequency of the output signal Fout of the acceleration/deceleration circuit changes based on input data set to a data register/control portion. The data register/control portion is configured to acquire data Sc set to an initial value register which is data for deciding a start-up frequency Fs, then read out the calculation result drawn by an accelerator/decelerator 4 upon receipt of an acceleration/deceleration request signal Sr from a timing generation circuit.
The clock output circuit disclosed by the aforementioned Japanese Unexamined Laid-open Patent Publication, however, is still complex in structure and only available to adjust acceleration a specified target frequency, resulting in difficulty in accelerating or decelerating a stepping motor to various target frequencies at different accelerations and lack of versatility.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.